The present invention relates to systems for forming permanent copies of cathode-ray tube images and, in particular, such a system that employs a diffraction grating face plate which for each image disperses to predetermined focal regions light rays of corresponding wavelengths which sequentially expose a region of a scrolled light-sensitive medium to form a composite color copy of the image.
Systems for making permanent copies of cathode-ray tube images are known. For example, U.S. Pat. No. 3,679,824 of Gibson, Jr. describes a system for providing copies of information stored on a cathode-ray storage tube. The Gibson system includes copying apparatus that is provided with a scanning mechanism operatively associated with a moveable light-sensitive surface which is adapted to provide a permanent copy of the image.
In the Gibson system, successive portions of an image to be copied are moved across a display screen at a speed synchronous to the movement of the light-sensitive surface, which is disposed adjacent the screen. An image that is larger than the screen can be scrolled across the screen to produce in the similarly scrolled light-sensitive surface a reconstructed representation of an entire image. This system suffers from two major disadvantages, of which one is the need for a fiber optic focusing material, which is relatively expensive, to present to the light-sensitive surface a focused reproduction of the image and the other is the inability to produce color copies of color images.
U.S. Pat. No. 4,309,720 of Denham describes a system for converting an electrical signal that defines a refreshed raster-scan image into an permanent hard copy representation of the image. The system divides each image into plural segments, each segment having three color components. Successive segments of the raster-scan image are scrolled across a display screen of a cathode-ray tube whose target structure comprises three adjacent strips of different phosphor materials. A light-sensitive medium is scrolled across the display screen at the same rate and is successively exposed to each color component of each segment of the image.
The Denham system also suffers from the disadvantage of requiring the use of a fiber optic focusing material over the display area defined by the phosphorescent strips to present to the light-sensitive medium a focused reproduction of the image appearing within the display area.
U.S. Pat. No. 4,172,259 of Lowe describes a graphic recording apparatus that is compensated for record medium velocity changes. The Lowe system includes a fiber optic cathode-ray tube over which a light-sensitive medium is scrolled to form a copy of the image appearing in the display area of the cathode ray tube. The velocity compensating mechanism is described with reference to a line scan fiber optic cathode-ray tube that is capable of producing monochrome copies of the cathode-ray tube image.
An article authored by J. E. Wurtz, "Color Display and Recording With CRTs," Electro-Optical Systems Design, April 1981, pp. 42 and 43, briefly describes a line scan fiber optic cathode-ray tube as a means for obtaining color copies of a cathode-ray tube image. The article also suggests other means for generating light in three colors. These include the use of three narrow phosphor stripes positioned on the face plate of the cathode-ray tube or the use of a prism positioned in the optical path of light passing through a white phosphor to separate the colors. The Wurtz article contemplates only systems using fiber optic cathode-ray tubes as a means to provide a focused image in the display area.